Thermal management system

ABSTRACT

A thermal management system for operating near a temperature T. The system includes a sheet-like spacer having a plurality of passageways. A degassed working fluid is disposed as a liquid within the passageways of the spacer. A flexible and substantially impermeable sheet-like envelope forms a sealed compartment enclosing the spacer and the degassed working fluid at an absolute pressure that is approximately equal to the vapor pressure of the working fluid at equilibrium with liquid phase of the working fluid at the temperature T. The spacer, the working fluid and the envelope form a sheet-like thermal management system. In some embodiments the spacer is a flexible spacer and the envelope is a flexible envelope and the sheet-like thermal management system is a flexible sheet-like management system. In some embodiments the envelope is a rigid structure.

GOVERNMENT RIGHTS

The United States Government has rights to this invention pursuant to contract number DE-AC05-000R22725 between the United States Department of Energy and UT —Battelle, LLC.

FIELD

This invention relates to the field of thermal management systems. More particularly, this invention relates to devices for heating or cooling objects or persons by evaporation and condensation.

BACKGROUND

Heat stress has been a problem for military personnel since armies first operated in hot environments. Greek and Roman soldiers suffered from the heat in addition to the physical burden imposed by the weight of body armor and weapons whenever they fought in the Middle East or Southwest Asia. Today's warrior faces the same problem; a combination of physical workload and lack of cooling diminish the performance of highly trained individuals. For example, during the 1967 war between Israel and Egypt, the Egyptian army sustained over 20,000 heat casualties.

The advent of chemical and biological warfare has created an increased thermal burden by requiring the use of cumbersome or encapsulating garments. Military units and First Responders attempting to conduct missions in such garments, particularly in hot environments, often find their physical endurance greatly diminished and cognitive functions impaired. Available resources are often overtaxed by demands on logistic support for such things as excess potable and cooling water, and the increased numbers of personnel that are needed to accommodate extended rest periods that are required by exhausted personnel.

Similar problems exist in the civilian sector. For example, foundry workers, chemical plant operators, and warehouse workers often find themselves limited in their capacity to perform tasks in hot climates. Mining is notorious for placing sometimes life-threatening thermal burdens on deep shaft miners (e.g., South African gold miners). On the other hand, extremely cold environments produce similar difficulties. Divers, winter sportsmen, and persons living in northern latitudes often encounter cold conditions that may induce hypothermia.

Various approaches have been adopted to reduce heat and cold stress. The simplest approach has typically been to impose well defined work/rest cycles which limit an individual's exposure time and allow for cooling-off (or warming-up) rest periods. This is often successful in minimizing fatigue and illness but severely constrains productivity and may threaten successful task performance if manpower is limited. Passive cooling systems have sometimes been employed to mitigate heat stress. Passive cooling systems, such as water-soaked clothing items or ice vests are a comparatively low cost approach but provided only a limited amount of cooling. Passive heating systems such as extra layers of clothing are also comparatively low cost, but they loose their effectiveness if they become moist with perspiration which can in fact contribute to hypothermia if the temperature drops.

There are many further needs for efficiently heating and cooling materials and objects such as electronic components, car seats, plants, and animals that are often inadequately addressed by present techniques. What are needed therefore are improved systems for providing thermal management of persons and objects in very hot and very cold environments.

SUMMARY

The present invention provides a thermal management system for operating near a temperature T. The system includes a substantially incompressible flexible sheet-like spacer that has a plurality of passageways. The system also includes a working fluid that has a liquid phase and a vapor pressure, and at least a portion of the working fluid is disposed within the passageways of the spacer. There is a flexible and substantially impermeable sheet-like envelope that forms a sealed compartment enclosing the spacer and the working fluid at an absolute pressure that is approximately equal to the vapor pressure of the working fluid at equilibrium with liquid phase of the working fluid at the temperature T. The spacer, the working fluid and the envelope form a flexible sheet-like thermal management system.

Another embodiment provides a thermal management system for operating near a temperature T, and this system has a sheet-like spacer having a plurality of passageways and a sheet-like wick disposed adjacent the spacer. There is a working fluid that has a liquid phase and a vapor pressure, and at least a portion of the working fluid is disposed as a liquid within the wick and disposed as a vapor in the passageways of the spacer. The system also has a substantially impermeable sheet-like envelope that forms a sealed compartment enclosing the spacer and the working fluid at an absolute pressure that is approximately equal to the vapor pressure of the working fluid at equilibrium with liquid phase of the working fluid at the temperature T. The spacer, the wick, the working fluid and the envelope form a sheet-like thermal management system.

A further embodiment provides a thermal management garment system that has a sheet-like spacer having a plurality of passageways. There is a working fluid that has a liquid phase and a vapor phase, and at least a portion of the working fluid is disposed within the passageways of the spacer. The system also includes a flexible and substantially impermeable sheet-like envelope that forms a sealed compartment enclosing the spacer and the working fluid at a temperature and pressure where the liquid phase and the vapor phase are near equilibrium. The thermal management garment system is configured to conform to a human body and transfer heat to or from portions of the body.

A method is provided for fabricating a thermal management system. The method includes a step of disposing a spacer in a compartment in a substantially impermeable envelope having a port that provides a passageway having at least one channel for transporting at least one fluid into an out from the compartment. The method also includes a step of adjusting the air pressure in the compartment through the port. In a further step, degassed working fluid is injected through the passageway in the port. The method concludes with closing the passageway.

Another method embodiment is provided for fabricating a thermal management system. In this method a spacer and a frangible pouch containing a working fluid are disposed in a substantially impermeable envelope having a compartment. The air pressure is adjusted in the compartment and the compartment of the envelope is sealed. The frangible pouch is broken to release the working fluid inside the compartment.

BRIEF DESCRIPTION OF THE DRAWINGS

Various advantages are apparent by reference to the detailed description in conjunction with the figures, wherein elements are not to scale so as to more clearly show the details, wherein like reference numbers indicate like elements throughout the several views, and wherein:

FIG. 1 is a somewhat schematic and partially cut-away perspective illustration of one embodiment of a thermal management system.

FIG. 2A is a magnified image of a structure of material that may be used as a spacer in a thermal management system.

FIG. 2B is an illustration of an alternate material that may be used as a spacer in a thermal management system.

FIG. 3 is a somewhat schematic cross-sectional illustration of a thermal management system.

FIG. 4 is a somewhat schematic cross-sectional illustration of the thermal management system of FIG. 3 showing fluid flow when the system is adapted for cooling.

FIG. 5 is a somewhat schematic cross-sectional illustration of the thermal management system of FIG. 3 showing fluid flow when the system is adapted for heating.

FIG. 6 is a somewhat schematic front view illustration of a thermal management system installed with a garment and configured for cooling a person wearing the garment.

FIG. 7 is a somewhat schematic front view illustration of a thermal management system installed with a garment and configured for warming a person wearing the garment.

FIG. 8 is a somewhat schematic view of a thermal management garment system as worn by a person.

FIG. 9 is a phase diagram for water showing certain operational conditions for use of water as a working fluid in a thermal management system.

FIG. 10 illustrates a test apparatus for evaluating the performance of a thermal management system.

FIG. 11 is a graph illustrating the performance of a thermal management system.

DETAILED DESCRIPTION

In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings, which form a part hereof, and within which are shown by way of illustration the practice of specific embodiments of thermal management systems and embodiments of methods for fabricating a thermal management system. It is to be understood that other embodiments may be utilized, and that structural changes may be made and processes may vary in other embodiments.

Disclosed herein are various embodiments of closed-loop evaporation/condensation thermal management systems that may, for example, be used to transport heat away from heat sensitive regions of the human body (such as the chest) to less heat-sensitive regions (such as the extremities). Embodiments are also provided for heating regions of a human body or other object. Graded levels of cooling and heating may be provided. Various embodiments may provide moderate cooling in hot environments or moderate heating in cold environments without a supplemental heat sink or heat source device. In preferred embodiments for heat reduction situations, a supplemental cold pack is applied to the thermal management system at a location where heat should be withdrawn in order to provide enhanced cooling for objects in contact with other locations on the thermal management system. In preferred embodiments for relief from cold conditions, a supplemental hot pack is applied to the thermal management system at a location where heat should be added in order to provide enhanced warming.

Many embodiments employ a flexible bag that encloses a spacer material and some embodiments employ a wicking material. In a typical system a vacuum is pulled on the bag and the bag is backfilled with a working fluid such as water or a fluorocarbon refrigerant. This process creates a vapor space where the working fluid is near the liquid/vapor equilibrium state at the pressure and temperature in the bag. Since the working fluid is in a meta-stable state, any heat added at one surface location on the system will cause evaporation of the fluid at that location, thereby cooling that region. The resulting vapor migrates to cooler regions of the bag where it condenses, warming those regions. The condensed fluid migrates to the warmer region to complete the cycle. In effect the system operates to moderate temperature differences across the surface of the thermal management system.

If a cold object (i.e., a heat sink) is placed in contact with an area of the thermal management system, vapor in that region will condense and reduce pressure in the system, thus causing the fluid to boil in the warmer areas and thus cool the warmer areas. The system will uniformly cool across the areas that are not in direct contact with the heat sink. The system also operates in a warming mode without adjusting the configuration of the system. If a warm object (i.e., a heat source) is placed in contact with an area of the thermal management system, liquid in that region will evaporate and increase the pressure in the system, thus causing the fluid to condense in cooler areas and warm the cooler areas. The system will also uniformly warm the areas that are not in direct contact with the hot source.

One embodiment of a thermal management system 10 is illustrated in FIG. 1. Thermal management system 10 incorporates a flexible and substantially impermeable sheet-like envelope 20. As used herein, the term “flexible” refers to a material that can be manually warped without using tools and the material may be warped without breaking. As used herein the term “sheet-like” refers to a structure that is thin in comparison with its length and breadth. A sheet-like object may be flat or curved in three-dimensional space. In the embodiment of FIG. 1 the envelope 20 is fabricated as a first sheet of aluminized MYLAR® 22 that is bonded to a second sheet of aluminized MYLAR® 24 at a bond line 26. MYLAR® is the registered trademark of DuPont Tejjin Films for a specific family of plastic sheet products made from Polyethylene Terephthalate (PET) resin. The generic term for this material is polyester film. A portion of the first sheet 22 is deleted in FIG. 1 in order to illustrate features that physically underlie the first sheet 22. In actual application the first sheet 22 is substantially congruent with the second sheet 24 and the bond line 26 extends all around the edge of the envelope 20. The bond can be either a heat seal of the first and second sheets (22 and 24) sheets or a chemical bonding agent that is used to “glue” the sheets together.

A sealed compartment 28 is formed between the first sheet 22 and the second sheet 24. “Sealed” means that the compartment 28 is configured to substantially prevent the leakage of ambient air back into the compartment if the compartment has been evacuated or leakage out from the compartment if the compartment has been pressurized. A bond line width 30 of approximately 15 mm is generally helpful in substantially eliminating the leakage into or out from the compartment 28. Typically the compartment 28 will be evacuated (i.e., pumped down to a pressure that is less than ambient atmospheric pressure) but in some applications where a high vapor pressure working fluid is used, the compartment 28 ultimately may be pressurized relative to ambient atmospheric pressure.

In embodiments where the compartment 28 is evacuated, a substantially incompressible flexible sheet-like spacer material 32 may be disposed in the compartment 28. The spacer material 32 has a plurality of passageways 34 that permit the flow of liquids and vapors through its bulk mass. In this embodiment the compartment 28 is evacuated and the spacer 32 is substantially incompressible, meaning that under the differential pressure of the ambient atmosphere compared with the evacuated pressure of the compartment 28, the spacer 32 does not collapse to an extent that closes off a significant portion of the passageways in the spacer 32. The spacer 32 is flexible and sheet-like. A flexible sheet-like wick 36 is typically disposed between the spacer material 32 and one of the sheets (in this embodiment, the second sheet 24) that forms the sealed compartment 28.

A working fluid 40 is disposed in the compartment 28 of the envelope 20. At least a portion of the working fluid 40 is disposed as a liquid within the passageways of the spacer 32. The working fluid 40 may comprise water, a mixture of water and another fluid such as ammonia, an alcohol such as methanol or isopropanol, a fluorocarbon, or other refrigerant material, The amount of working fluid that is used depends primarily upon the surface area of one exterior side of the envelope 20, not including the area formed by the bond line width 30. For example, if one external side of the envelope 20 has a surface area (excluding the surface area formed by the bond line width 3) that is referentially defined in units of cm², then the preferred volume of water is between approximately 0.40 and 0.65 cm³ per cm² of surface area. However, a volume of water between approximately 0.20 and 1.3 cm³ per cm² of surface area may be used in some applications, and in some applications a volume between approximately 0.10 and 2.6 cm³ per cm² of surface area may be used.

It is beneficial that the working fluid 40 be degassed while it is in its liquid phase, so that substantially no gas is entrapped in the working fluid when the working fluid is disposed in the compartment 28. If not removed by degassing, entrapped gas, such as air, is released from the working fluid over time and reduces the vacuum in the compartment and interferes with the gas/liquid phase changes of the working fluid. The working fluid may be degassed by, for example, pulling a vacuum over the fluid or boiling the fluid before disposing it in the compartment 28. If boiling is used, the working fluid 40 at its boiling temperature may then be injected into the compartment 28.

A port 50 may be provided in the thermal management system 10. The port 50 may be similar to a medical port that is used to intravenously administer medications to patients. The port 50 has a passageway having at least one channel for transporting fluids into and out from the compartment. The port 50 may be configured to permit evacuation of air from the compartment 28 through the passageway and may be configured to inject the working fluid 40 into the compartment 28 through the passageway. The port 50 is typically configured so that it can be closed (airtight) after working fluid 40 is disposed in the compartment 28 and air is evacuated from the compartment 28

.In an alternate embodiment, the working fluid 40 may be provided in a pouch with a frangible seal, and the pouch may be inserted into the compartment 28. Typically the working fluid is degassed prior to sealing the working fluid 40 in the pouch and the pouch does not have any head space. After the pouch is placed in the compartment 28 the air may be evacuated from the compartment 28 using a vacuum pump hose or similar system, and the compartment 28 of the envelope 20 may be sealed. The frangible seal in the pouch may then be broken using pressure from outside the compartment 28 so that the working fluid is released inside the compartment 28. Among the advantages of this system are (1) there is no need to backfill the compartment 28 with working fluid 40 and (2) a vacuum may be pulled on the compartment 28 without accidentally pulling out the working fluid 40.

After the working fluid 40 is disposed in the compartment 28 and a substantial portion of the air is evacuated from the compartment 28, dimples 52 may be formed on the surface of the first sheet 22 and the second sheet 24 as a result of the evacuating process. The dimples 52 conform substantially to surface features in the spacer 32.

FIG. 2A illustrates a web material 60 that may be used as a spacer (such as spacer 32 in FIG. 1) in a thermal management system. The web material 60 is shown at approximately 50× magnification in FIG. 1. The web material 60 is made from fibers 62 that are bonded together at crossing points by an adhesive 64. The fibers 62 may be made from various materials such a spun polypropylene or nylon. The adhesive may be a resin type adhesive or similar adhesive. 3M SCOTCH-BRITE™ High Strength Grade A Medium (sold by 3M corporation as Product ID 048011-16068-9) is an example of such material. SCOTCH-BRITE™ Clean and Finish Grade A coarse (ID 048011-16807-4) is another material that may be used as web material 60.

Some fiber materials, particularly nylon, absorb water. Consequently if nylon is used as a spacer material and water is used as the working fluid, some of the water in a thermal management system may absorbed by the nylon and is therefore not readily available for the evaporation/condensation cycle. Similarly, other working fluids may be absorbed by other materials that may be used as spacers. To counter this condition, extra working fluid may be injected into the envelope of the thermal management system, or the spacer may be pre-saturated with the working fluid prior to disposing the spacer in the envelope of the thermal management system. Here the term “pre-saturated” means that the spacer material has been treated with the working fluid 40 prior to being disposed in compartment 28 until the fibers of the spacer material 32 are saturated. Pre-saturated does not mean that the passageways of the spacer are filled with the working fluid.

FIG. 2B illustrates an alternate structure for a spacer, a bubble mat 70. The bubble mat 70 includes a plurality of bubbles 72 that are filled with a gas 72 (typically air). The bubbles 72 are of sufficient strength and are spaced closely enough together to maintain passageways between the bubbles when the bubble mat 70 is installed in an evacuated envelope of a thermal management system. The material that forms the bubbles 72 and the seal around each bubble 72 are substantially impermeable to the gas 74 that fills the bubbles, so that the gas 74 does not leak from the bubbles 72 when the bubble mat is disposed in a thermal management system. In an alternate embodiment, a stiff sponge-like material having a surface contour similar to contour of the bubble mat 70 may be used as a spacer in a thermal management system.

FIG. 3 illustrates an alternate embodiment of a thermal management system 100, shown in a cross-sectional view. The thermal management system 100 has a substantially impermeable sheet-like envelope 110 with sealed edges 112. The envelope 110 forms a sealed compartment 114, and the envelope 110 may be formed from a flexible material such as polyolefin, polyester, or MYLAR® films, or from a material that forms a rigid or a semi-rigid structure. A semi-rigid structure is particularly desirable in embodiments where the compartment 114 is pressurized. A sheet-like spacer 116 having a plurality of passageways is enclosed in the compartment 114 together with a working fluid 118. The thermal management system 100 also includes a sheet-like wick 120 that is configured to transport the liquid working fluid 118 within the compartment 114. The sheet-like wick 120 may be a fabric material, such as MILLIKEN® 70 denier polyester tricot knit with wicking surface treatment (style number 692439).

In some embodiments the envelope 110 may be substantially rigid, meaning that under the differential pressure of the ambient atmosphere compared with the evacuated pressure of the compartment 114, the envelope 110 is not significantly deformed.

FIG. 4 illustrates the flow of working fluid 118 during one type of operation of the thermal management system 100. In the embodiment of FIG. 4, a heat sink 130 is applied to a location on the surface of the thermal management system 100. The heat sink 130 is in thermal contact with the envelope 110 of the thermal management system 100. The thermal contact permits heat flow from the envelope 110 to the heat sink 130. The heat sink 130 may be a chemical pack, a phase-change-material pack, an ice pack, or a similar device. A heat source 132 heats a different location on the surface of the thermal management system 100 compared with the location of the heat sink 130. The heat source 132 is in thermal contact with the envelope to permit heat flow from the heat source 132 to the envelope 110. The heat source 132 may be a portion of a human body, an electronic component, or some other source of heat. In operation, the heat source 132 causes the working fluid 118 to evaporate to a working vapor at a path 140. The evaporated working vapor transverses the spacer 116 along a path 150 toward the heat sink 130. The heat sink 130 condenses the evaporated working vapor to a working liquid at path 160. The sheet-like wick 120 transports the working liquid 118 back to the region of the heat source 132 along path 170. In embodiments that do not incorporate a sheet-like wick 120, gravity may be used to transport the liquid working fluid 118 to the region of the heat source 132. Note that the evaporation process at path 140 increases the pressure in that vicinity of the compartment 114 and the condensation process at path 160 lowers the pressure in that region of the compartment 114. Those pressure differentials motivate the flow of working fluid 118 through the compartment 114 of the thermal management system 100.

In the thermal management system 100 a wick 120 is typically employed if the thermal management system 100 is operated in a fashion in which gravity cannot assist the flow of liquid working fluid 118 from cold source (heat sink 130) to the heat source 132. For example, if the heat source 132 is located at the bottom of the heat pipe and the heat sink 132 is at the top of the heat pipe, then gravity will naturally return the working fluid 118 in its liquid phase from the heat sink 130 to the heat source 132. However, if the positions of the heat sink 130 and heat source 132 are reversed (with respect to the pull of gravity) with the heat source 132 on top and the heat sink 130 on bottom, then gravity cannot assist the flow of the working fluid 118 in liquid phase from cold to hot and a wick is typically used to move the liquid working fluid 118 from the heat sink 130 to the heat source 132.

FIG. 5 illustrates the flow of working fluid 118 during another type of operation of the thermal management system 100. In the embodiment of FIG. 5, a heat source 180 is applied a location on the surface of the thermal management system 100. The heat source is in thermal contact with the envelope 110 of the thermal management system 100. The heat source 180 may be a chemical pack, a phase-change-material pack, or a similar device. A heat sink 182 removes heat from the system at a different location on the surface of the thermal management system 100. The heat sink 182 is in thermal contact with the envelope 110 of the thermal management system 100. The heat sink 182 may be a portion of a human body or some other object that is to be warmed. In operation, the heat source 180 causes the working fluid 118 to evaporate to a vapor at a path 140. The evaporated fluid transverses the spacer 116 along a path 150 toward the heat sink 182. The heat sink 182 condenses the evaporated working fluid to a liquid at paths 160. The sheet-like wick 120 transports the liquid working fluid 118 back to the region of the heat source 180 along path 170. In embodiments that do not incorporate a sheet-like wick 120, gravity may be used to transport the liquid working fluid 118 to the region of the heat source 180. Note that the evaporation process at path 190 increases the pressure in that vicinity of the compartment 114 and the condensing process at paths 210 lowers the pressure in that region of the compartment 114. Those pressure differentials motivate the flow of working fluid 118 through the compartment 114 of the thermal management system 100.

FIG. 6 illustrates an embodiment of the thermal management system 100 in a garment 190 where the thermal management system 100 is used to cool a person wearing the garment 190. The elements illustrated in FIG. 6 correspond to the same elements as described for FIG. 4. FIG. 7 illustrates an embodiment of the thermal management system 100 in a garment 192 where the thermal management system 100 is used to warm a person wearing the garment. The elements illustrated in FIG. 7 correspond to the same elements as described for FIG. 5. In embodiments of a thermal management system that do not incorporate a wick and that is used to warm a person, benefit may be achieved by placing the heat source (e.g., 180 in FIG. 7) at location toward the bottom of the garment so that gravity feeds the condensed working fluid back to the heat source.

FIG. 8 illustrates a human 200 wearing a garment 210. The garment 210 has a thermal garment system 220 that is configured to conform to the human's 200 body and to transfer heat to or from portions of the body. The thermal garment system 220 is typically configured like the thermal management system 100 of FIGS. 3 through 7. The thermal garment system 220 has an upper portion 230 and a lower portion 240. There is a first retaining portion 250 for retaining a heat source or a heat sink in the upper portion 230 of the thermal garment system 220, and a second retaining portion 260 for retaining a heat source or a heat sink in the lower portion 240 of the thermal garment system 220. When the thermal garment system 220 is used to warm the human 200 a heat source may be placed in the second retaining portion 260. The heat source will vaporize the working fluid in the thermal garment system and the human's 200 body will condense the vapor to liquid, particularly in the upper portion 230 of the thermal garment system 220. In this configuration gravity may be used to move the condensed liquid working fluid down to the heat sink in the second retaining portion 260, so that a wick may not be employed in the thermal garment system 220. In an alternate configuration where the thermal garment system 220 is used to cool the human 200 a heat sink may be placed in the first retaining portion 250. Heat from the human's 200 body, particularly in the lower portion 240 of the garment system 220, will evaporate the working fluid in the thermal garment system 220, and the working fluid vapor will move through the thermal garment system to the heat sink, where it will be condensed by the heat sink in the upper retaining portion 250. In this configuration gravity may be used to move the condensed liquid working fluid down to the portions of the thermal garment system 220 where the warmth of the human's 200 body vaporizes the working fluid, so that a wick may not be employed in the thermal garment system 220.

As previously noted, thermal management systems include a working fluid that evaporates and condenses to achieve the desired thermal transfers. Each thermal management system has a operating temperature regime that centers around a particular temperature, which for illustrative purposes may be designated as temperature “T.” It is desirable to operate a thermal management system along the vapor-liquid equilibrium curve of the working fluid near temperature “T.” For many applications temperature “T” is about 80° F. (approximately 27° C. or 300K). In such applications water may be used as the working fluid. FIG. 9 illustrates a phase diagram for water. FIG. 9 illustrates that for operation around 80° F. (approximately 300K), a thermal management system using water as the working fluid should operate near the region labeled 300. That region corresponds to a vapor pressure of about 35,600 Pa (356 millibars or 26.7 mm Hg). Thus a thermal management system using water as the working fluid and evacuated to an absolute pressure of about 35,600 Pa may be used to moderate temperatures around 80° F. (approximately 27° C.).

EXAMPLE

FIG. 10 illustrates a test apparatus 400 for evaluating thermal management systems. The test apparatus includes a stand 410 that supports a heating pad 420 that is powered through an electrical connection 430. A thermocouple 440 is placed on the heating pad 420 and connected to a temperature logging instrument 450. One end of a thermal management system 100 was placed over the heating pad 420 with a cooled area 460 of the thermal management system 100 being exposed for cooling. In this test the thermal management system 100 was constructed from two aluminized MYLAR® sheets. A continuous heat-sealed seam around the perimeter of the sheets formed a compartment that enclosed a SCOTCH-BRITE™ spacer and two layers of MILLIKEN® 70 denier polyester tricot knit as a wick. Approximately 65 ml of degassed water was disposed in the compartment.

In the test setup of FIG. 10 the cooled area 460 of the thermal management system 100 may be exposed to a cooling source 470 and/or simply exposed to ambient atmosphere. To begin a test, the heating pad was allowed to heat up to a temperature that is above ambient room temperature. The thermal management system 100 is then placed over the heating pad 420 and the temperature logging is started.

FIG. 11 presents a sample of a time-phased temperature measurement for the test setup of FIG. 10, recorded as a trace 500 by the temperature logging instrument 450 of FIG. 10. Initially the temperature recorded at the thermocouple 440 was 125° F., which in this test was the temperature of the heating pad before the thermal management system 100 was placed over the heating pad 420. As seen from the trace 500, when the thermal management system 100 was placed on the heating pad 420 (a point 510 on trace 500), the temperature began dropping as the thermal management system 100 removes heat from the heating pad. The temperature at the heating pad 420 stabilized at about 95° F. in about 15 minutes. Then at a point 520 of the trace 500, an ice pack was applied as the cooling device 470 to the vicinity of region 460 of the thermal management system 100. The temperature measured at the thermocouple 440 then proceeded to drop further, stabilizing at about 85° F. approximately 30 minutes after the test started.

In summary, embodiments disclosed herein provide various embodiments for thermal management systems and methods for fabricating thermal management systems. The foregoing descriptions of embodiments of this invention have been presented for purposes of illustration and exposition. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments are chosen and described in an effort to provide the best illustrations of the principles of the invention and its practical application, and to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled. 

1. A thermal management system for operating near a temperature T, the system comprising: a substantially incompressible flexible sheet-like spacer having a plurality of passageways; a working fluid having a liquid phase and a vapor pressure, wherein at least a portion of the working fluid is disposed within the passageways of the spacer; a flexible and substantially impermeable sheet-like envelope that forms a sealed compartment enclosing the spacer and the working fluid at an absolute pressure that is approximately equal to the vapor pressure of the working fluid at equilibrium with liquid phase of the working fluid at the temperature T; wherein the spacer, the working fluid and the envelope form a flexible sheet-like thermal management system.
 2. The thermal management system of claim 1 wherein the spacer further comprises at least one material selected from the group consisting of spun fibers and bubble mat.
 3. The thermal management system of claim 1 wherein the working fluid comprises a liquid that is degassed.
 4. The thermal management system of claim 1 wherein the thermal management system further comprises a flexible sheet-like wick configured to transport liquid working fluid within the compartment.
 5. The thermal management system of claim 1 wherein the thermal management system further comprises a sheet-like wick configured to transport liquid working fluid within the compartment.
 6. The thermal management system of claim 1 wherein the envelope comprises aluminized polyester sheet material.
 7. The thermal management system of claim 1 wherein the working fluid comprises a volume of water.
 8. The thermal management system of claim 7 wherein the sheet-like package has a surface area referentially defined in units of cm², and the volume of water is between approximately 0.10 and 2.60 cm³ per cm² of surface area.
 9. The thermal management system of claim 1 further comprising an element disposed in thermal contact with a portion of the envelope, the element selected from the group consisting of a heat sink and a heat source.
 10. A thermal management system for operating near a temperature T, the system comprising: a sheet-like spacer having a plurality of passageways; a sheet-like wick disposed adjacent the spacer; a working fluid having a liquid phase and a vapor pressure, wherein at least a portion of the working fluid is disposed as a liquid within the wick and disposed as a vapor in the passageways of the spacer; a substantially impermeable sheet-like envelope that forms a sealed compartment enclosing the spacer and the working fluid at an absolute pressure that is approximately equal to the vapor pressure of the working fluid at equilibrium with liquid phase of the working fluid at the temperature T; wherein the spacer, the wick, the working fluid and the envelope form a sheet-like thermal management system.
 11. The thermal management system of claim 10 wherein the spacer further comprises at least one material selected from the group consisting of spun fibers and bubble mat.
 12. The thermal management system of claim 10 wherein the working fluid comprises a liquid that is degassed.
 13. The thermal management system of claim 12 wherein the working fluid comprises a volume of water and the sheet-like package has a surface area referentially defined in units of cm², and the volume of water is between approximately 0.10 and 2.60 cm³ per cm² of surface area.
 14. The thermal management system of claim 10 further comprising an element disposed in thermal contact with a portion of the envelope, the element selected from the group consisting of a heat sink and a heat source.
 15. A thermal management garment system comprising: a sheet-like spacer having a plurality of passageways; a working fluid having a liquid phase and a vapor phase, wherein at least a portion of the working fluid is disposed within the passageways of the spacer; a flexible and substantially impermeable sheet-like envelope that forms a sealed compartment enclosing the spacer and the working fluid at a temperature and pressure where the liquid phase and the vapor phase are near equilibrium; wherein the thermal management garment system is configured to conform to a human body and transfer heat to or from portions of the body.
 16. The thermal management garment system of claim 15 further comprising a retaining portion for receiving a heat source for heating the wearer.
 17. The thermal management garment system of claim 16 wherein the garment system has an upper portion and lower portion and the heat source is positioned in the lower portion.
 18. The thermal management garment system of claim 15 further comprising a retaining portion for a heat sink for cooling the wearer.
 19. The thermal management garment system of claim 18 wherein the garment system has an upper portion and a lower portion and the heat sink is positioned in the upper portion.
 20. The thermal management system of claim 15 further comprising an element disposed in thermal contact with a portion of the envelope, the element selected from the group consisting of a heat sink and a heat source.
 21. A method of fabricating a thermal management system, the method comprising the steps: (a) disposing a spacer in a compartment of a substantially impermeable envelope having a port that provides a passageway having at least one channel for transporting at least one fluid into and out from the compartment; (b) adjusting the air pressure in the compartment through the passageway in the port; (c) injecting a degassed working fluid into the compartment through the passageway in the port; and (d) closing the passageway.
 22. The method of claim 21 wherein step (c) comprises injecting a working fluid at its boiling temperature through the port.
 23. A method of fabricating a thermal management system, the method comprising: (a) disposing a spacer in a substantially impermeable envelope having a compartment; (b) disposing a frangible pouch containing a working fluid in the compartment; (c) adjusting the air pressure in the compartment; (d) sealing the compartment of the envelope; and (e) breaking the frangible pouch to release the working fluid inside the compartment. 